That cool black snack may be Instagram-worthy, but watch out.

Black is the new rainbow, at least in food trends. Black ice cream, black macarons, black pasta, black beverages, black croissants ... they're the foodie's latest Instagram darling. How does that hue end up in food? Sometimes, squid ink does the job, but activated charcoal powder is becoming an increasingly popular way to color food black, like in this ice cream recipe.

What is activated charcoal?

Activated charcoal powder is a manufactured substance, the "byproduct of slowly burnt wood ... or coconut shells treated with oxygen, a process which renders it highly porous and nonpolar, allowing it to adsorb (that is, bind to, as opposed to absorb) hydrophobic toxins and odors from gases or liquids up to 1,000 times its weight," according to Organic Life.

Activated charcoal powder is used in food and beauty products. (Photo: Akvals/Shuttertock)

Traditionally, activated charcoal has been used for medicinal purposes, particularly to help treat some types of poisonings or drug overdoses. WebMD says it's also used to treat cholestasis during pregnancy, prevent gas, reduce high cholesterol and prevent a hangover — although the effectiveness of activated charcoal is not proven for those uses and there has been limited research.

Activated charcoal is also used to whiten teeth, to detoxify the body and it's put in facial masks to draw out dirt and oils, although there's more anecdotal evidence than scientific evidence that these uses are effective.

For example, a recent study published in the British Dental Journal found that charcoal-based toothpastes that claim to whiten teeth are a "marketing gimmick." Instead, the charcoal-based products can actually increase the risk of tooth decay and staining, reports the BBC.

Dangers of activated charcoal

In most instances, the small amount ingested in an occasional treat made with black charcoal is harmless, but there are some risks involved with the substance under certain circumstances, particularly if ingested regularly. WebMD says that when taken by mouth, activated charcoal can cause black stools, black tongue, vomiting or diarrhea or constipation. In serious cases, it may cause gastrointestinal blockages.

A bigger concern, however is how activated charcoal may interact with medications. Activated charcoal should not be consumed if you're taking drugs used for constipation. It can also reduce the effectiveness or prevent the absorption of drugs like acetaminophen, digoxin, theophylline, tricyclic antidepressants and birth control pills. If you're on any of these medications, check with your doctor before using activated charcoal.

And if you're on a date, it's probably best to skip the black foods altogether unless you think black teeth and a black tongue are romantic.

Editor's note: This story has been updated since it was originally published in August 2017.